A variety of parallel optical communications devices exist for simultaneously transmitting and/or receiving multiple optical data signals over multiple respective optical data channels. Parallel optical transmitters have multiple optical transmit channels for transmitting multiple respective optical data signals simultaneously over multiple respective optical waveguides (e.g., optical fibers). Parallel optical receivers have multiple optical receive channels for receiving multiple respective optical data signals simultaneously over multiple respective optical waveguides (e.g., optical fibers). Parallel optical transceivers have multiple optical transmit channels and multiple optical receive channels for transmitting and receiving multiple respective optical transmit and receive data signals simultaneously over multiple respective transmit and receive optical waveguides (e.g., optical fibers).
For each of these different types of parallel optical communications devices, a variety of different designs and configurations exist. A typical layout for a parallel optical communications device includes a first mounting device, such as a printed circuit board (PCB), a flex circuit, or a leadframe, which is used to mount a plurality of active optical devices (e.g., laser diodes and/or photodiodes) and one or more integrated circuits (ICs) (e.g., a laser diode driver IC, a receiver IC, a controller IC). The combination of these electrical components and the first mounting device on which they are mounted is typically referred to as the electrical subassembly (ESA). A second circuit board, such as a PCB, a ball grid array (BGA), or the like, that is external to the parallel optical communications device, is used for mounting one or more other ICs and other electrical components. The second circuit board and the first mounting device are electrically connected to each other to provide electrical connections between the electrical components of the ESA and the electrical components mounted on the second circuit board.
Similar configurations are used for parallel optical receivers, except that the ESA has a plurality of photodiodes instead of laser diodes and a receiver IC instead of a laser diode driver IC. An ESA of a parallel optical transceiver typically has laser diodes, photodiodes, a laser driver diode IC, and a receiver IC, although one or more of these devices may be integrated into the same IC to reduce part count and to provide other benefits.
A typical parallel optical communications device also includes an optical subassembly (OSA), which holds optical elements for coupling light between the laser diodes and/or photodiodes of the ESA and the ends of respective optical fibers that are held within a connector that mechanically couples with the OSA. The OSA is secured to the ESA. There are sometimes mating features on the OSA and on the ESA that allow the OSA to be coupled to the ESA in a way that limits movement of the OSA relative to the mounting device to provides some degree of coarse alignment between the optical elements of the OSA and the laser diodes and/or photodiodes of the ESA. Prior to coupling the OSA to the ESA, an adhesive material, such as epoxy, for example, is placed at one or more locations on one or more surfaces of the OSA and/or of the ESA. After the OSA has been coupled to the mounting device, and prior to the adhesive material hardening, an alignment process is typically used during which relative movement between the OSA and the ESA is produced until a determination is made that the optical elements of the OSA are precisely aligned with the laser diodes and/or photodiodes of the ESA. The OSA and the ESA are then tightly held in the aligned position until the adhesive material has been cured and otherwise hardens.
There are several challenges associated with coupling the OSA to the ESA, precisely optically aligning the OSA with the laser diodes and/or photodiodes of the ESA, and securing the OSA to the ESA in the precisely aligned position. In order to manufacture the parallel optical communications modules with high volume, the OSA must be coupled, precisely aligned, and secured to the OSA very quickly, e.g., in less than one minute. In addition, after the OSA has been secured to the ESA, very little or no movement of the OSA and ESA relative to each other should occur over the life of the parallel optical communications device, or else the precise optical alignment may be lost. Precise optical alignment is critical to having good signal integrity, and thus good overall performance. Often times, a customer attaches a heat sink device to the parallel optical communications device, which causes forces to be exerted on the OSA and/or on the ESA. If the bond that is formed by the adhesive material is not sufficiently strong, the exertion of such forces over months or years can result in very slow movement of the OSA and ESA relative to each other, sometimes referred to as creeping. Of course, such movement can result in the precise alignment needed being lost, resulting in a degradation in performance.
In addition to the issues associated with aligning the OSA with the ESA and securing them together, heat dissipation is a major consideration in parallel optical communications devices. In the aforementioned parallel optical communications devices, some portion or portions of the mounting device of the ESA has one or more heat sink devices thereon that dissipate heat generated by the electrical components of the ESA. Often times, the customer provides its own heat sink device, which the customer secures to the mounting device of the ESA. The heat sink device is typically secured to the mounting device of the ESA by a thermally conductive epoxy material. One of the problems associated with securing the heat sink device to the ESA is that the customer typically exerts a relatively large force on the heat sink device during this process, which, in turn, is exerted on the ESA. Components of this force may also be exerted on the OSA. Such forces can result in movement of the OSA and the ESA relative to each other, which can result in the precise alignment between the OSA and the ESA being lost.
The aforementioned heat sink devices have various shapes or configurations, but have the same general purpose of receiving heat generated by the ICs and active optical devices of the ESA and absorbing and/or spreading out the heat such that the heat is moved away from the ICs and active optical devices. Heat generated by the ICs can detrimentally affect the performance of the parallel optical communications device. For example, in parallel optical transmitters and transceivers, the laser diode driver ICs generate very large amounts of heat in producing the high speed signals that drive the laser diodes. If adequate measures to dissipate this heat are not taken, the heat can detrimentally affect the performance of the laser diode ICs, which are typically placed in relatively close proximity to the laser diode driver IC. Heat dissipation considerations are even more important in parallel optical communications device due to the large number of channels and associated electrical circuitry.
In addition, there is an ever-increasing need to decrease the size of parallel optical communications devices and to increase the number of channels in parallel optical communications devices. In order to meet these needs, the layout of a parallel optical communications device should be efficient in terms of space utilization, highly effective at dissipating heat, and protective of signal integrity. As the number of channels and the associated electrical components increases, the amount of heat that must be dissipated also increases, which emphasizes the need for a highly effective heat dissipation configuration. Also, as the dimensions of the parallel optical communications device decrease, the space between the electrical components decreases. This reduced space between components also emphasizes the need for a highly effective heat dissipation configuration in order to prevent heat generated by one component from detrimentally affecting another.
In addition to the need for highly effective heat dissipation configurations in parallel optical communications devices, the OSA should be secured to the ESA in a way that ensures that there will be no movement of the OSA and ESA relative to each other. In general, parallel optical communications devices are non-hermetically, or semi-hermetically, sealed devices. As indicated above, typically, an adhesive material such as epoxy is used to secure the OSA to the ESA while the OSA and the ESA are held in tight alignment. This adhesive bond tends to be structurally weak, which can result in movement of the OSA and the ESA relative to each other. Likewise, as indicated above, an adhesive material such as a thermally conductive epoxy is often used to secure the heat sink device to the mounting device of the ESA. This adhesive bond is also relatively structurally weak, which can result in movement of the heat sink device and the ESA relative to each other. As indicate above, such movement can result in forces being exerted on the OSA, resulting in movement of the OSA and the ESA relative to each other. Such movement can, as indicated above, result in the precise optical alignment between the OSA and the ESA being lost, which can result in a degradation in signal quality.
Accordingly, a need exists for a parallel optical communications device that is configured with an extremely strong bond between the OSA and the mounting device of the ESA to prevent any movement between the OSA and the ESA, and which does not impede the heat dissipation qualities of the parallel optical communications device. A need also exists for a method for quickly aligning and securing the OSA to the mounting device of the ESA in a way that creates an extremely strong bond at the interface between the OSA and the ESA mounting surface and that enables very precise optical alignment to be achieved between the OSA and the ESA.